Modded a NTSC-U NUS-CPU-03 Nintendo 64 some time ago for RGB and had a SCART cable to test it with finally. Thing is, it is in black and white only.
I've had red show up alone and blue will mix with red for a lovely purple but green simply didn't seem to do anything on its own until I redid the soldering on my SCART->BNC adapter and found it now did black and white only. The occasional yellow hue would take over. The cable is fine as the owner sent me a SNES jr to mod for RGB and the SNES jr looks lovely in RGB on the same displays (Sony PVM).
There is an amp inside using a Texas Instruments chip with RGB tapped from C124, C125, and C126. I realize I could tap RGB directly from the video encoder but this seems like a better idea.